Polycarbonates

ABSTRACT

LINEAR POLYCARBONATE RESINS CONTAINING MANY PENDANT ESTER GROUPS AND POSSESSING THE GENERAL STRUCTURAL FORMULA   HO-(1,4-PHENYLENE)-C(-A)(-(CH2)N-COO-R)-(1,4-PHENYLENE)-   O-CO-O)N-(1,4-PHENYLENE)-C(-A)(-(CH2)N-COO-R)-   (1,4-PHENYLENE)-OH   WHEREIN:   A IS A RADICAL SELECTED FROM THE GROUP CONSISTING OF -H, -CH3, AND -C6H5; R IS AN ALKYL GROUP CONTAINING ONE TO EIGHTEEN CARBON ATOMS AND N IS AN INTEGER IN THE RANGE OF 40 TO 70 INCLUSIVE,   ARE CONVERTED TO THE CORRESPONDING LINEAR POLYCARBONATE RESINS CONTAINING A LARGE NUMBER OF PENDANT HYDROXYL GROUPS ONLY BY REDUCTION OF THE ESTER GROUP WITH DIBORANE (B2H4). THE HYDROXYL GROUPS THUS PRODUCED IN THE POLYCARBONATE MOLECULAR CHAIN ARE USEFUL AS GRAFTING AND CROSS-LINKING SITES FOR FURTHER REACTION WITH ORGANIC AND ORGANIC-INORGANIC MOIETIES TO PROVIDE MODIFIED POLYCARBONATES WITH ENHANCED PHYSICAL PROPERTIES.

Patented Mar. 2, 1971 3,567,686 wherein: Ronald E. f%fig gg gfig ;gggg G. Gardlund A is a radical selected from the group consisting of -H,

Utica, Mich., assignors to General Motors Corpora- T and C6H5 tion Detroit, Mich R is an alkyl group containing one to eighteen carbon No Drawing. Filed Aug. 27, 1969, Ser. No. 853,495 atoms- Int. Cl. C08g 17/13 d Us. CL 260 47 3 Claims These esters are prepared by the reactlon of a deslre alcohol with a suitable bis-phenol acid. The alcohol is a member of the series of saturated aliphatic alcohols running from methyl alcohol up to and including stearyl al- ABSTRACT OF THE DISCLOSURE 10 cohol. The bis-phenol acid is prepared in a known man- Linear polycarbonate resins containing many pendant ner by the condensation of phenol with the suitable keto ester groups and possessing the general structural foracid or keto ester such as levulinic acid. The prepared m-ula bis-phenol acid ester is then reacted with an equimolar t a t -t @rQ- H2). ((131192 COOR OOOR wherein: amount of phosgene in a suitable solvent at about room 0 temperature to produce a hydroxy terminated polycar- A Is g lsg i ggg the group conslstm" of bonate containing a large number (40 to about 70) of 3 s pendant ester groups. Upon 1solat1on of the esterlfied R 5 3; 222 group contalmng one to elghteen carbon 2, polycarbonate from its reaction medium, the pendant ester groups are chemically reduced to CH OH groups n 1s an integer 1n the range of 40 to 70 inclusive, with diborane (BZHS), preferably in tetrahydrofuran are converted to the corresponding linear polycarbonate solvent. The pendant hydroxyl groups thus formed are resins containing a large number of P ndant hydroxyl useful for cross-linking sites such as by reaction with digTOUPS oIlly y reduction of the ester gr p With isocyanates or grafting with various organic and organicborane (B H The hydroxyl groups thus produced in inorganic moieties. the polycarbonate molecular chain are useful as grafting These and other objects and advantages of our invenand cross-linking sites for further reaction with organic tion will become more apparent in view of a detailed and organic-inorganic moieties to provide modified polydescription thereof which follows.

carbonates with enhanced physical properties. Because of the inherent structure of the starting monomers (derivatives of bis-phenol) used to produce polycarbonates, it has heretofore been impossible to synthe- This invention relates to linear polycarbonates and size a polycarbonate polymer containing a carbonate remore particularly it relates to linear polycarbonates havpeating unit along with a repeating hydroxyl group. There ing reactive pendant hydroxyl groups on the molecular is no general method of introducing repeating hydroxyl chains thereof. groups directly into the polymer because if such groups It is an object of the present invention to provide polyare present in the bis-phenol monomer they are concarbonate-type synthetic resins containing a large number sumed by the phosgene during polymerization. At the of hydroxyl groups along the molecular backbone which same time, prior to our invention, there were no techgroups are reaction sites for subsequent grafting or crossniques of introducing repeating pendant hydroxyl groups linking operations with respect to the polycarbonate resin.

into a for-med polymer. In general, the process aspects of It is another object of the present invention to provide our invention involve the chemical reduction of known a method of forming a linear polycarbonate containing linear polycarbonates containing repeating pendant ester pendant hydroxyl groups in up to about 90% of the groups to the corresponding linear carbonate containing monomeric units along the molecular chain thereof, repeating pendant hydroxyl groups by treatment of the which method involves the treatment of known polycar- Q polymer with diborane. The diborane only slowly attacks bonate resins containing pendant ester groups with dithe carbonate linkages and therefore does not drastically borane (B H to effectively and selectively reduce the degrade the polymer chain during the reduction reaction. ester groups to hydroxyl groups without substantially de- Reduction by other means, such as lithium aluminum grading the polymer itself. hydride, basic hydrolysis or acidic hydrolysis does not In accordance with a preferred embodiment of our give the desired result. In the case of lithium aluminum invention these and other objects are accomplished by hy for eXample, y Slight ester reduction Occurs first providing a bis-phenol a id ester. Thi bis-phenol but substantial carbonate reduction takes place and deacid ester possesses the general tructural fo la; gradation of the polymer is extensive. Neither basic nor acidic hydrolysis effects any substantial ester reduction, A but basic hydrolysis degrades the polymer severely. Therefore, these common methods for reducing ester grou s are not applicable to polycarbonate system.

In general, the starting material for our process is a COOR linear polycarbonate containing pendant ester groups of the type depicted in the following structural formula:

i ii A L I I wherein:

A is a radical selected from the group consisting of H,

CH3 and C6H5;

R is an alkyl group containing one to eighteen carbon atoms, and

n is an integer in the range of 40 to about 70 inclusive.

These are known polymeric substances (see e.g., US. 3,132,118) prepared by reacting the above-described bisphenol acid ester with a substantially equimolar amount of phosgene in a known manner. The bis-phenol acid ester is prepared by esterification of the corresponding bis-phenol acid, which is, in turn, formed by condensation of phenol with a suitable keto-acid or keto-ester such as those specified above.

The formation of the bis-phenol acid ester is carried out by reacting an alcohol of the saturated aliphatic series containing one to eighteen carbon atoms inclusively and a bis-phenol acid preferably of the type represented by the following general structural formula:

OlI

where A is a radical selected from the groups consisting of H, CH and C H An excess of the alcohol is employed and the esterification reaction is conducted by heating the acid alcohol mixture to a temperature in the range of 80 to 120 C. Water is formed in the esterification reactions and should be continually removed. A solvent or solvent system may be used for the esterification reaction medium and if the reaction is conducted at reflux temperature, water can be removed by phase separation from the refluxing water immiscible solvent. Suitable esterification solvents are benzene, toluene, or xylene. Since acidic conditions favor the esterification reaction, catalytic amounts of acids such as dry hydrochloric acid are preferably used during the esterification. Esterification is generally complete in a period of from five to twelve hours. At the end of the esterification the solvent is removed by vacuum distillation at temperatures of less than 120 C. The resulting bis-phenol acid ester can be purified by recrystallization from hydrocarbon solvents. All of the alcohol should be removed from the ester so that a subsequent polymerization reaction is not abruptly terminated.

The bis-phenol acid ester is polymerized to a polycarbonate product containing repeating pendant ester groups by reaction with phosgene. The reaction is best carried out in a solvent or solvent system. Suitable solvents such as ether, benzene, toluene, and chlorinated solvents such as dichloromethane may be employed as the reaction medium. The phosgene and bis-phenol acid ester are reacted in equimolar amounts. The bis-phenol acid ester is dissolved in the solvent and the phosgene is bubbled through the solution in the form of a gas. If the phosgene is metered into the solution it is possible to determine when an approximately molecular equivalent amount of the material has been added to the solution. An excess of phosgene may be employed without harm to the polymeric product but an excess of the acid ester will reduce the average molecular weight of the product due to incomplete reaction.

The reaction between phosgene and the bis-phenol acid ester is accelerated by the use of a strong base Which serves to eliminate the hydrogen chloride byproduct. Preferably, organic bases such as pyridine, quinoline or the like are employed, However, inorganic bases such as sodium hydride and potassium hydride may be used.

It is preferred that the exothermic reaction be conducted at about room temperature, generally in the range of 10 to 40 C., and preferably in the range of about 2025 C. The reaction temperature may be maintained within the preferred range by employing cooling water to withdraw heat from the reaction mixture.

At the completion of the reaction, when an equimolar or small excess of phosgene has been absorbed by the reaction solution, the linear polycarbonate product is recovered from the solvent system. Hydrochloric acid salts of organic bases formed during the reaction are precipitated and removed by filtering. Water can then be mixed with the solvent to precipitate the polymer therefrom in the form of a flocculant precipitate. The polycarbonate containing a pendant ester group in every monomeric unit is soluble in tetrahydrofuran, dimethylformamide and chloroform and may be reprecipitated from these solvents for purposes of purification. This ester group containing linear polycarbonate is the starting material for the process aspect of our invention.

A linear polycarbonate containing a pendant hydroxyl group in every monomeric unit is then formed by reduction of the pendant ester groups of the polycarbonate thus far produced. This is accomplished by reduction of the pendant ester groups to the hydroxyl groups by using diborane (B H generated in situ (see Zwerfel and Brown, Organic Reactions, l3, 1 (1963)) or purchased commercially in a tetrahydrofuran solvent. A specific example will serve to illustrate the invention.

Two molar equivalents of phenol were condensed with levulinic acid ll (Cll's-O-ClleCIhC O OH) to form 4,4-bis-(p-hydroxyl phenyl) pentanoic acid. This acid was esterified with ethyl alcohol to form the ethyl ester thereof. The polycarbonate of the ethyl ester of the bis-phenol acid was then formed by a reaction of 0.1 mole of the ester with a 10% molar excess of phosgene in 250 ml. of anhydrous pyridine under a nitrogen atmosphere. The polymer was precipitated into water, washed with hot water and vacuum dried. The polymer Was reprecipitated by pouring a chloroform solution thereof into methanol. In this instance the number average molecular Weight of the polymer was 13,000 as determined by membrane osmometry at 45.0 C. in sym-tetrachloroethane.

Three grams of the above polycarbonate containing pendant ester groups was dissolved in 250 ml. of dry tetrahydrofuran. To this stirred solution at 0 C. was slowly added 50 ml. of a diborane solution in tetrahydrofuran (1.0 molar in EH over a one hour period. Stirring at 0 C. Was continued for twenty-four hours. The excess diborane was destroyed by adding 100 ml. of a 50:50 methanolztetrahydrofuran mixture. The volume of the solution was reduced to 50 ml. and the polymer was precipitated therefrom by pouring into a 5% aqueous hydrochloric acid solution. The precipitated polymer was washed with water and dried overnight to yield 2.9 grams of reduced polymeric product. Infrared analysis of the product indicated virtually complete reduction of the ester group along with an increase in hydroxyl absorption but no decrease in carbonate absorption. The pendant COOR groups on about of the monomeric units were reduced to pendant CH OH groups. The number average molecular weight of the product Was 6500. This means that on the average the polymer chains were split in half during the reduction reaction. This is entirely acceptable when it is recognized that the product can be cross-linked by means of reaction with the pendant hydroxyl group produced by our process.

Our process may be employed to reduce linear polycarbonate resins containing pendant ester groups along the molecular chains thereof wherein the ester groups are of aliphatic alcohols containing one to eighteen carbon atoms and the products of our process may be represented gentively high molecular weight containing reactive hydroxyl erally by the structural formula: groups along the backbone of the molecular chain thereof.

A O A Q i Q Q Ho-- -C- CO -C- OH L I .l I

((I3H2)2 (CH2)2 CHQOH CHzOH wherein I While our invention has been described in terms of a A 15 Tadlcal Selected from the group 3 and few specific embodiments thereof, it will be appreciated a 5 and that other forms of the invention could readily beadapted is an integer in the range of to by one skilled in the art. Therefore, the scope of our in- The polycarbonate product of our invention contains vention is to be considered limited only by the following a plurality of pendant hydroxyl groups which are useful claims. for both cross-linking and grafting purposes. We have ob- We claim: served that there may be a reduction of up to 50% in 15 1. A method of forming polycarbonate-type, synthetic average molecular Weight in going from the ester polyresins containing a plurality of reactive hydroxyl groups carbonate to hydroxyl polycarbonate which is due both to along the molecular chains comprising providing a polyelimination of the pendant alkyl groups forming part of carbonate of the type A 0 A E@ l (300R COOR the ester and to some minor degradation of the polymer A is a radical selected from the group consisting of -H, itself. We have observed no more than a 50% reduction CH and C H R is an alkyl group containing one to in the number average molecular weight of the polymer eighteen carbon atoms and n is an integer in the range of following ester reduction with diborane. This would indi- 40 to 70 inclusive and reducing the repeating pendant cate that on the average no more than one carbonate C0OR groups thereon to 2 groups with linkage is being attacked by the diborane while some 40 boraneto 70 ester group per molecule are being reduced to hy- Afi 9 formmg a hneal' Polycarbonate Tesm droXyl groups. Our polymeric product typically has an contammg r epeatmg Pendant hyfiroxyl F P along average molecular weight in the range of 6000 to 10,000. leciular Chams thereof Compnsmg Provldmg bls'phenol The properties of this pendant hydroxyl group containing acld ester of the type polycarbonate may be modified by cross-linking by re- 39 action with a diisocyanate, isocyanate terminated polyurethane prepolymers, diacids, or acid terminated polymers such as polyesters and the like. Another use for our inven- 000R tion is in the coating of polycarbonate optical members 40 wherein A is a radical selected from the group consisting such as lenses and 1n Windshields wherein our hydroxyof H, CH and C H and R is an alkyl group con- 0I1t aining Polycarbonate is F pp to the Surface of a taining one to eighteen carbon atoms, polymerizing said ventional polycarbonate article for the purpose of further bi h l id ester ith hosgene to fo a li polybonding abrasion resistant materials to our novel hydroXycarbonate containing repeating pendant ester groups as containing polycarbonate through the hydroxyl groups. depicted in the structural formula:

A O A 112 (cam COOR COOR This use of our novel polycarbonate is more completely wherein A and R have the said values and n is an integer described in a copending application Ser. No. 874,771, in the range of 40 to 70 inclusive, and reducing the pendfiled Nov. 7, 1969. ant COOR groups to CH OH groups by reaction with Diborane (B H is the only known suitable reducing diborane (B H material for producing polycarbonate plastics containing 3. Linear polycarbonates containing repeating pendant hydroxyl groups along the main backbone by reduction of hydroxyl groups along the molecular chains thereof conpendant ester groups. When an attempt was made to treat sisting essentially of the type generally represented by the the polycarbonate employed in the above example With structural formula:

A o A "Q Q 1 Q Q IIO- o OCO O OH I HM E 02 0112011 CHzOH lithium aluminum hydride at room temperature, no sigwherein A is a radical selected from the group consisting nificant reduction of the ester groups was obtained. When of H, CH and -C H and n is an integer in the another sample of the polycarbonate prepared from a range of 20 to 35 inclusive phenolic acid ester was treated With lithium aluminum hydride solution in tetrahydrofuran at reflux, almost comlete degradation of the polycarbonate was experienced,

i he average molecular Weight being reduced from 23,700 UNITED STATES PATENTS to 750. 3,285,875 11/1966 Bottenbruch et al. 260-47 An attempted hydrolysis of the pendant ester groups in sulphuric acid apparently had no eifect on the pendant SAMUEL BLECH, m y Examiner ester groups as an infrared analysis of the treated polymer showed no diminishment of the ester peak. However, treatment with diborane produces a polymeric product of rela- 117--138.8; 260-30.4, 32.6, 33.8, 858, 860

References Cited 

